Many initial deployments of packet-based telephony networks are using ATM as the core packet technology. The preferred architecture for packet telephony uses media gateways that interface to existing telephony equipment like telephones or TDM-based trunk or access lines and perform the necessary adaptation to a packet format. Media gateways are controlled by media gateway controllers that perform call processing and service processing and control the setup and teardown of connections between media gateways. Connections are established over a generic packet core network that can be used to provide a variety of services relating to data, video and voice.
Currently, asynchronous transfer mode (ATM) networks are favored to support voice communications, as these packet networks are sufficiently mature to meet the stringent Quality of Service (QoS) requirements associated with telephony communications. However, the extensive acceptance of the Internet Protocol for most other applications is indicative of the fact that voice communications may ultimately be carried using the Internet Protocol. Many network operators deploying ATM-based telephony solutions have expressed the desire to evolve their ATM-based investment toward IP. Although many evolution and transition paths are possible, none so far have been able to preserve the investment made in ATM equipment or to provide a smooth migration from ATM to IP while keeping the telephony services operational. For example, media gateways have traditionally only supported either voice over IP (VoIP) or voice over ATM (VoATM). With the rigidity of current architectures, the transition from one format to another requires replacing one network with another, with little opportunity for a gradual transition. Accordingly, there is a need for a way to transition from one network technology to another in a reliable and cost effective manner. Further, there is a need to transition from a VoATM format to VoIP in a reliable and efficient manner.